Our invention relates generally to a data storage apparatus for use with magnetic record media such as, typically, those in the form of flexible disks. More particularly, our invention pertains to such a magnetic data storage apparatus, or disk drive according to common parlance, that has an electromagnetic head assembly of the familiar tunnel erase or equivalent type for trimming or erasing the opposite marginal edge portions of each record track as data is written thereon. Still more particularly, our invention concerns a system in such a magnetic data storage apparatus for defeating inconveniences arising from a difference in the polarity of magnetization on the blank spaces created by the erase heads of different disk drives between the record tracks on the flexible magnetic disk or like record media.
The rotating disk data storage apparatus has been known which has a tunnel erase head assembly, as disclosed for example in U.S. Pat. No. 4,853,799 to Aikawa. The tunnel erase head assembly is an integral combination of a read/write head and a pair of tunnel erase heads. As the read/write head creates a record track on the disk, the pair of tunnel erase heads trim off the opposite marginal edge portions of the track. The successive record tracks are therefore created with intervening spaces. These intervening spaces make it possible for the read/write head to subsequently read the data on the tracks in the face of some mistracking.
There has, however, been a problem left unsolved with the tunnel erase head assembly. As indicated in the Aikawa patent, supra, the common tunnel erase coil of erase heads is energized and deenergized under the control of a tunnel erase signal which is derived from the write gate signal. As is well known in the disk drive art, the write gate signal is fed from the host system to enable the read/write head to write on the magnetic disk. If the read/write gap and erase gaps of the tunnel erase head assembly are spaced longitudinally or circumferentially of each annular record track, as is usually the case, then the tunnel erase signal is obtained by delaying the write gate signal a length of time corresponding to the spacing between read/write gap and erase gaps. Thus, as the read/write head starts writing data on any track, the tunnel erase coil is energized with a direct current for trimming the marginal edges of the data track being created.
The problem arises from the fact that the tunnel erase signal, like the write gate signal, is a binary digital signal. Consequently, switched on and off by this digital tunnel erase signal, the tunnel erase coil is energized with a direct erase current that has so far had an instantaneously rise and an instantaneous fall. Such instantaneous rise and fall of the tunnel erase current would present no problem at all if the disk spaces created by the tunnel erase heads were magnetized in the same polarity. The fact is, however, that the polarity of disk magnetization by the tunnel erase heads is not standardized in the disk drive art but differs from one disk drive to another.
The widespread practice now is to put the same magnetic disk to use with two or more different disk drives. This same disk may therefore be tunnel erased in one polarity in one disk drive and in the other polarity in another. In that case the disk spaces between the record tracks will have parts (sectors) that are magnetized in one polarity and other parts that are magnetized in the other. Since the direct current flowing through the tunnel erase coil has hitherto risen and fallen instantaneously as aforesaid, an abrupt change has occurred in the polarity of magnetization from one part to another of any one space.
We object to such an abrupt change in the polarity of magnetization because the read/write head of the tunnel erase head assembly may subsequently scan the spaces as a result of mistracking. The read/write head will then produce a noise output that may interfere with the data to be retrieved. We will later discuss this inconvenience in more detail with reference to the accompanying drawings.